I have been interested in this thread for a while. However most high efficiency mini split units are running 300+v inverters from the line, which is contrary to you stating they use 48v. My Midea U (a dual inverter mini split on a common pan basically) uses 310v blower motors and compressor, and amazingly achieves 15btu/w.
I have tried reaching out to Alibaba.com sellers about 24v truck units but no one will provide data sheets or efficiency ratings. Best I can figure based on the given specs is ~10btu/w much like my old 110v Frigidaire 8000btu. Start up current may be a benefit in comparison to old style window units, but for a Midea U the 10% inverter losses is < 50% efficiency gain in btu output and the Midea unit starts extremely soft too the benefits weigh in favor of the Midea. The cost of these DC direct units also blows away the cost of an efficient window unit and a capable inverter. $349 Midea 8k window unit + 200 inverter and you'll still have some wiring money left.
I would order two of these tomorrow if the efficiency could match what exists here already. I would love to pitch in and assist in bringing up something more efficient if there is interest.